Changes in lipid patterns associated with neoplastic cell transformation are being studied in transplantable animal tumors (Novikoff hepatomas, series of Morris hepatomas, Ehrlich ascites tumors), in human cancer tissues, and in Novikoff and other tumor cells grown in tissue culture. Emphasis is placed on the structure and distribution of unusual lipid constituents whose changes can be correlated with rapid proliferation or degree of differentiation. Interest is being focused on diol lipids and lactic acid-derived lipid constituents. Diol phospholipids have attracted attention because of their strongly lytic activity. Lactic acid-derived lipid constituents are of interest as they can amount to up to 20 percent of certain phosphorylcholine fractions of tumors. The structures of these unusual constituents will be studied in detail and their distribution in tumor, host and control tissues, in plasma membranes, and in other subcellular fractions will be determined. Their pathways of biosynthesis and catabolism will be established in in vivo and in vitro systems.